fix event test

Author: cgutsche

test/model_parsing.jl

@@ -350,7 +350,7 @@ end
     u0 = [model.x => 10, model.y => 0, model.z => 0]
 
     prob = ODEProblem(model, u0, (0, 5.0))
-    sol = solve(prob, tstops = [1.5])
+    sol = solve(prob, Tsit5(), tstops = [1.5])
 
     @test isequal(sol[model.y][end], 1.0)
     @test isequal(sol[model.z][end], 2.0)
@@ -568,4 +568,4 @@ end
 
     @test Equation[ternary_true.ternary_parameter_true ~ 0] == equations(ternary_true)
     @test Equation[ternary_false.ternary_parameter_false ~ 0] == equations(ternary_false)
-end
+end